Evaluating Superconductors through Current Induced Depairing

The phenomenon of superconductivity occurs in the phase space of three principal parameters: temperature T, magnetic field B, and current density <i>j</i>. The critical temperature <inline-formula> <math display="inline"> <semantics> <msub> <mi>T</mi> <mi>c</mi> </msub> </semantics> </math> </inline-formula> is one of the first parameters that is measured and in a certain way defines the superconductor. From the practical applications point of view, of equal importance is the upper critical magnetic field <inline-formula> <math display="inline"> <semantics> <msub> <mi>B</mi> <mrow> <mi>c</mi> <mn>2</mn> </mrow> </msub> </semantics> </math> </inline-formula> and conventional critical current density <inline-formula> <math display="inline"> <semantics> <msub> <mi>j</mi> <mi>c</mi> </msub> </semantics> </math> </inline-formula> (above which the system begins to show resistance without entering the normal state). However, a seldom-measured parameter, the depairing current density <inline-formula> <math display="inline"> <semantics> <msub> <mi>j</mi> <mi>d</mi> </msub> </semantics> </math> </inline-formula>, holds the same fundamental importance as <inline-formula> <math display="inline"> <semantics> <msub> <mi>T</mi> <mi>c</mi> </msub> </semantics> </math> </inline-formula> and <inline-formula> <math display="inline"> <semantics> <msub> <mi>B</mi> <mrow> <mi>c</mi> <mn>2</mn> </mrow> </msub> </semantics> </math> </inline-formula>, in that it defines a boundary between the superconducting and normal states. A study of <inline-formula> <math display="inline"> <semantics> <msub> <mi>j</mi> <mi>d</mi> </msub> </semantics> </math> </inline-formula> sheds unique light on other important characteristics of the superconducting state such as the superfluid density and the nature of the normal state below <inline-formula> <math display="inline"> <semantics> <msub> <mi>T</mi> <mi>c</mi> </msub> </semantics> </math> </inline-formula>, information that can play a key role in better understanding newly-discovered superconducting materials. From a measurement perspective, the extremely high values of <inline-formula> <math display="inline"> <semantics> <msub> <mi>j</mi> <mi>d</mi> </msub> </semantics> </math> </inline-formula> make it difficult to measure, which is the reason why it is seldom measured. Here, we will review the fundamentals of current-induced depairing and the fast-pulsed current technique that facilitates its measurement and discuss the results of its application to the topological-insulator/chalcogenide interfacial superconducting system.

Abstract licence: CC BY

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